The present invention concerns a device for the longitudinal alignment of plate elements within an indeed station of a machine working them for the packaging production. In such a machine, the plate elements or paper or cardboard sheets are successively taken from the bottom of a pile and brought flat towards a line of working stations such as printing stations, cutting and waste stripping stations, before being piled up again in a delivery station.
At the infeed, the sheets are stored on a pile supporting plate equipped with an automatic vertical shifting chain device, so that the upper end of the pile remains the same during the infeed of the sheets into the operating machine. Lifting suction cups take the sheets one by one from the top of the pile and carry them towards carrier suction cups. The carrier suction cups have a back and forth horizontal movement in order to carry each sheet towards a feed table where the plate elements can thus be arranged tilewise.
A way of carrying out each sheet conveyance from the input of the feed table to the first processing station is to jointly use driving belts and pressure rollers which allow maintaining the sheet on the conveyor belt and carrying it to the front of the first working station. Each sheet is then removed to the next stations by gripper bar chains.
The device related in this invention is useful at the infeed station, right before the infeed table. To ensure correct functioning of the machine, it is necessary, on one hand, to guarantee the correct alignment of the leading edge of each plate element introduced so that it is not slanted and, on the other hand, to keep step in the speed with which those elements which are laid on the feed table. This last condition defmes the longitudinal location of the sheet on the conveyor belt, that is its position in the way of its travelling, so that the gripper bar can catch it easily when it comes. This speed can be physically estimated by the existing space between two leading edges of two successive plate elements on the feed table. The setting of a device for the alignment of the leading edge of the sheet makes it possible to perform both these two conditions as this device is working in synchronism with the production speed of the machine.
A device allowing the longitudinal alignment of the sheets usually comprises a transverse shaft connecting, from end to end, the width of the feed table. This shaft is settled slightly below the highest level of the sheet maintained by the carrier suction cups. When it is vertically installed, a blade extending along the transverse shaft and secured to it is acting as a stop for the leading edge of the sheet and is allowing thus its alignment. The shaft being synchronized with the production rate of the machine, it is moved by a repetitive rotation from 0 to 45 degrees, so that the blade is acting as a flap alternatively in a closed vertical position, and in an open oblique position which allows in this last case the travelling of the sheet in the feed table.
Several devices of this kind are known up to date but a few of them consider a subordinate problem involved with the inital state of the sheets at the time they have to be introduced into the production machine. The organic paper or cardboard sheets used in the packaging industry are particularly sensitive to the ambient conditions under which they are dealed with or stored. The moisture rate of the ambient air is one of the main settings significantly acting on the mechanical, dimensional and especially geometrical specifications of the sheet. Although the sheet is initially flat, it will often curve itself due to the variations of the hygrometrical rate of the ambient for example, but also due to a printing left on one of its sides. This phenomenon of curving is usually called xe2x80x9cwarpxe2x80x9d in this technical field. The warp is especially involved in the corrugated board sheets and is all the more present as the thickness of the sheet is large or as the quality of materials used in the two sides of the sheet is different; what is often the case for the corrugated packaging boards having a high printing quality. It is obvious that the phenomenon of warp does not mean inevitably a symmetrical defect compared to one of the two symmetrical axis of the sheet. It may occur in fact that the sheet shows a more significant curve in its left part that in its right part or inversely.
Using strongly warped sheets onto a production machine means various problems, particularly at the time of the infeed of the sheet into the feed table, but also during the alignment of the leading edge of the sheet right before its infeed. The sheet being usually seized by the suction cups in its middle, if we introduce a strongly warped sheet in the feed table it generates an inconvenience on lateral parts of the sheet which will be deemed to knock against the leading edge of the feed table. Indeed, if we consider the concave curve of the sheet, the edge of the side parts of these sheets is located right below the infeed level, which corresponds to the central part of the sheet held by the suctions cups.
To overcome this problem, one can use tablets arranged on the leading part of the feed table such as they were shown in the patent CH 651""807. Comprising plates or bars curved downwise, these tablets make easier the infeed of the badly curved leading parts of such a warped sheet.
However, if strongly warped sheets must be used, a flap such as the one previously described is always standing in the way of their travelling. The edge parts of these warped sheets will indeed knock against the lateral parts of the opened flap, while risking to turn down the corners of the sheet. To face this problem, one can reduce the length of the flap by keeping only its central part so that the leading edges of the warped sheet can then travel easily thanks to the lateral release thus granted. This solution requires a division of the flap in several removable parts or in a multiplicity of segments, removable if required.
However, this option reveals a few disadvantages which are, on one hand, an unsuitable reduced alignment limited to the central part of the sheet which refers to the importance of its warp and, on the other hand, an additional handling which is to be achieved in a reduced space not easy to deal with, requiring thus the use of auxiliary tools for the assembly and the dismounting of the flap. Knowing that the warp of piled up sheets on a pile supporting plate at the infeed station varies according to the height of the pile, this option will require within the operation phase, on one hand, a permanent control of the travelling of the sheets over the opened flap and, on the other hand, many repeated manual handlings intended to control the length of this flap according to the curving rate of the sheets. These several operations involve thus frequent stops of the machine which are increasing the production cost.
The shape of the lateral guides supporting the infeed of the sheet rather changes according to the maximum release which offers, in its lateral parts, the device for the longitudinal alignment of the sheet. This release is inversely egual to the space occupied by the lateral parts of the flap when this one is intended to be of the necessary improvement allowing the travelling of warped sheets. More important is the release at the edges of the flap, better could be the travelling of the sheets and stronger could be their warp. But, on the contrary, larger is the length of the path of the leading edge of the sheet against the flap, better will be the alignment of the sheet and smaller will be the lateral release.
Up to this day, the machine operator was constrained to find the suitable option for the particular condition of these two opposite reports, so as generating the repeated and non-convenient adjustments such as those abovementioned.
To solve this problem, the aim of this invention is, for attaining the longitudinal alignment of sheets, a device with universal joints from which the movable stop flap shaft can be of a shape adapted to the curve of the leading edge of the warped sheet. To this end, the device of this invention comprises a device for longitudinal alignment of plates within an infeed station of a machine for working the plates. Two lateral brackets have a conveyor track for plates between them comprised of two plates that are folded down according to a line that is not perpendicular with respect to the shifting of the plates. The plates are advanced by at least two separated conveyor belts which run around pulleys and the pulleys for the belts are secured between immovable bearings located toward the input of the device. A protection plate is disposed at the leading edge of the plate above which flaps are movable. A transverse shaft connects the leading or entrance ends of the lateral brackets, and the shaft is rotatable in alternative directions between 0xc2x0 and 45xc2x0 synchronized with the production speed of the machine to allow successive alignment of the plates. The shaft is comprised of several links, which are shaft segments joined at universal joints. Each of the segments carries a respective one of the flaps. The ends of the shaft are supported in movable bearings in the lateral brackets.
The advantages resulting from this invention are mainly involved in the fact that such a device allows on one hand to carry out an alignment of the sheet on its nearly entirely leading edge, for a range of sheets affected with a significant warp (up to 4 to 5%), symmetrical or asymmetrical. On the second hand, the device according to the invention is able to stay definitively in the infeed station thanks to its particular tendency allowing it to easily modify its shape in order to be adapted to the convex shapes of the warped sheets. Advantageously, no part must be added to or removed from the flap of the aforesaid device, and no auxiliary tool is necessary to its setting which allows significant saved time during the preparation of the machine in the case of a new work. Finally, owing to a lack of existence, the risk to lose some parts of the flap can be completely removed in this new concept.
With an aim of defining a few words of the described position and the orientation of some parts within the machine with reference to the present invention, one will speak of xe2x80x9coperator""s sidexe2x80x9d and xe2x80x9copposite operator""s sidexe2x80x9d used as a reference to a side indicated with comparison to the longitudinal median axis of the machine. This option allows to avoid any confusion occurring with the conventional definitions left and right-hand side depending on the point of view of the observer. With the same idea, one will use the usual words xe2x80x9clongitudinalxe2x80x9d and xe2x80x9ctransversexe2x80x9d with references to the median axis of the machine whose position is determinded by the direction of the run of the plate elements. Finally, one will also specify that the words xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d are referring to the way of run of the plate elements of the machine in production.